The background of the invention is basically shown in the aforesaid U.S. Pat. No. 3,213,228 and in U.S. Pat. Nos. 2,179,099 (Nelson) and 2,777,032 (Burch) cited as references in U.S. Pat. No. 3,213,228.
U.S. Pat. No. 3,213,228 shows and describes a planar loop or blade of resilient sheet metal basically the same as that used in several embodiments in this invention. Briefly, it comprises two flat loops of generally U-shape, these loops being placed side by side. As so placed, the outer legs are longer than the inner legs, and the ends of the outer legs are joined by a cross-connection. The loop is stressed by spreading apart the inner legs, and as clearly described in that patent, the loop becomes unstable and occupies one of two stable positions. The thus stressed loop will snap with a snap action from one of these stable positions to the other stable position.
In the switch of U.S. Pat. No. 3,213,228 using this loop, the contacts are coaxial. Thus, the switch may be either a single pole, single-throw switch, or a single pole, double-throw switch.
Such a switch has desirable performance characteristics in regard to its motions, the force differentials required to operate it, and its snap action. However, in spite of the desirable results obtained by using the construction shown in U.S. Pat. No. 3,213,228, the invention thereof can be improved in certain respects by this invention.
Since prior art switches may be operated by relatively slowly moving means, the contact force being exerted by the snap-acting element decreases in such manner that, under some operating conditions, it will stay at or near zero value long enough to permit chattering of the switch contacts and possibly freezing thereof. There is, therefore, need of a snap-acting switch in which the contact pressure thereof, prior to actual contact separation, is maintained at a relatively high amount regardless of how slowly the operator actuates the switch.
In addition, in the snap closing of electrical contacts, bounce of the latter will generally occur. In many cases, such bouncing will cause freezing of the contacts and other deleterious effects. Therefore, there is need of a snap-acting switch in which simple and economic means are provided to minimize by several orders of magnitude the amount and duration of such bouncing.